The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
(1) Field of the Invention
This invention generally relates to trajectory control and more specifically to a method and apparatus for providing guidance parameters at launch that direct a pursuing vehicle from a launching vehicle to a target vehicle capable of evasive maneuvering after the target vehicle becomes alerted to the presence of the pursuing vehicle.
(2) Description of the Prior Art
The trajectory control of a pursuing vehicle can be classified as post-launch or pre-launch control. In post-launch control, guidance information is sent from the launching vehicle to guide the pursuing vehicle to the target. The following United States Letters Patent disclose such post-launch trajectory control systems:
U.S. Pat. No. 3,260,478 (1966) to Welti
U.S. Pat. No. 3,643,616 (1972) to Jones
U.S. Pat. No. 3,784,800 (1974) to Willoteaux
U.S. Pat. No. 5,319,556 (1994) to Bessacini
U.S. Pat. No. 5,436,832 (1995) to Bessacini et al.
The Welti patent discloses the control of a first object in dependence upon a position of a second object for collision or anti-collision purposes. A regulator, that controls the travel and includes a travel control member for the first object, receives positional information of the first and second objects as a pilot magnitude and a reference magnitude. One of the positional informations is delayed in dependence upon a timing interval proportional to the time change of the quotient of the distance information of the two objects. The regulator subsequently supplies an output magnitude to the travel control member that represents the time differentials between the angular co-ordinates of the first and second objects modified by a disturbance magnitude.
The Jones patent discloses a method and apparatus for guiding a torpedo along a collision course to a moving target ship. A control system on the launching vehicle sends guidance parameters over a communication cable to maintain a predetermined, substantially constant lead angle with respect to the target ship by adjusting torpedo speed as the torpedo travels toward an anticipated collision.
In the Willoteaux patent a trajectory control system calculates the distance between a moving body and other moving or stationary objects by taking account of the speeds and direction of each. The control system simulates a series of hypothetical trajectories diverging on either side of the actual trajectory until a hypothetical trajectory is determined which satisfies various imperatives. The system then instructs the moving body control system to change the linear and or angular speed thereof so that the moving body follows the latter trajectory.
The Bessacini patent discloses an adaptive trajectory apparatus and method for providing, after launch, vehicle control commands to steer an underwater vehicle launch from a vessel toward a contact. As commands produced by this system transfer between the launching vessel and the launched vehicle over a communications link.
The Bessacini et al. patent discloses a beam rider guidance system for directing a steerable object, such as a torpedo. The guidance system senses the bearing between a launching vehicle and a target vehicle and determines the bearing between the launching vehicle and the torpedo as it moves toward the target vehicle. Various error signals are then generated and classified into sensed linguistic variables based on membership functions of different sensed variable membership function sets to become fuzzy inputs to a controller that produces fuzzy control output linguistic variables and associated membership functions from a control output membership function set based upon logical manipulation of the fuzzy inputs. These fuzzy control output membership functions are converted into an output having an appropriate form for control, subject to optional constraint to prevent unwanted effects.
Other references of general interest in the field of trajectory control include:
U.S. Pat. No. 2,879,502 (1959) to Miller
U.S. Pat. No. 3,360,637 (1967) to Smith
U.S. Pat. No. 3,860,791 (1975) to Headle, Jr.
U.S. Pat. No. 4,323,025 (1982) to Fisher et al.
U.S. Pat. No. 5,355,325 (1994) to Uhlmann
As generally found in prior art post-launch control systems, a pursuing vehicle exits a launching vehicle. Control systems on the launching vehicle monitor the relative positions of the pursuing vehicle and a target and control the pursuing vehicle by the transfer of information between the launching vehicle and the pursuing vehicle over communications link. When the launching vehicle is a submarine and the pursuing vehicle is a torpedo, the communications link typically comprises a communications wire. If the pursuing vehicle is a missile the communications typically occurs over some radio link. In either case, post-launch control systems on the launching vehicle issue guidance parameters to guide the pursuing vehicle along some trajectory into a predetermined relationship with the target.
In a pre-launch system, the pursuing vehicle follows a predetermined trajectory after launch that may or may not be programmable prior to launch. However, with either type, the pursuing vehicle leaves the launching vehicle and travels along a known trajectory that may be simple or complicated. With torpedoes, missiles and the like, that may undergo pre-programmed maneuvers, the input guidance parameters may include gyro angles and time lapse signals. One time lapse signal represents the interval between the launch and the enablement of any instrumentation on the torpedo or missile such as an acoustic seeker on a torpedo.
In order to provide the most accurate pre-launch guidance parameters to the pursuing vehicle, it is necessary that the interval between the time a last estimate of target state is made and the time a pursuing vehicle is launched be quite short. It is during this interval that a prior art pre-launch system must produce the guidance parameters, and this interval has constrained the nature of the analysis required to produce such guidance parameters. For example, prior art pre-launch systems generally assume that the target will maintain a constant velocity even after the target becomes alerted to the presence of the pursuing vehicle. In actual practice, however, a target normally takes evasive action. With prior art pre-launch systems two or more pursuing vehicles travel along the calculated course and one or more offsets from that calculated course to take evasive maneuvers into account.
Therefore it is an object of this invention to provide a control method and apparatus for producing guidance parameters for use by a pursuing vehicle at launch that take into account potential evasive maneuvers of a target vehicle.
Another object of this invention is to provide a control method and apparatus for providing guidance parameters to a pursuing vehicle for use at launch that take into account a time at which the target vehicle becomes aware of the pursuing vehicle and the effect of any potential evasive maneuvers thereafter. Yet another object of this invention is to provide a control method and apparatus for providing guidance parameters to a pursuing vehicle for use at launch a short interval after a launching vehicle obtains an estimate of target vehicle state for producing an intercepting trajectory to an alerted target vehicle taking evasive action.
In accordance with this invention guidance parameters are provided to a pursuing vehicle prior to launch to place a pursuing vehicle on an intercept trajectory from a launching vehicle to a target vehicle with evasion capabilities. At the launching vehicle, the control method and apparatus determine the range, bearing, course and speed of the target vehicle and determine the guidance parameters based upon a first Cartesian coordinate system. The method and system receive a definition of target vehicle trajectory including a possible evasive maneuver defined on a second Cartesian coordinate system. This definition is converted from the second to the first Cartesian coordinate system. Iterative processing then uses this information on the first Cartesian coordinate system to plot the trajectories of the pursuing and target vehicles to an intercept in advance of the launch to generate the initial operating parameters for transfer to the pursuing vehicle.